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Amazon River outflow fights
greenhouse gasses

September
3 ,
2008 -- The
Amazon River plays a far more significant role in drawing carbon dioxide
from the atmosphere than previously understood, according to a new study
by a team of international scientists. Nutrients from the river's outflow
travel thousands of miles past the continental shelf, influencing the
carbon cycling in the tropical ocean.

A large sediment plume from the mouth of the Amazon River
expands outward into the tropical Atlantic Ocean. NASA

"We were surprised to find that a surface plume of fresh Amazon
water about the size of Texas had traveled so far out to sea," said Ed
Carpenter, professor of biology and Romberg Tiburon Center researcher,
a co-author of the study. "Our research showed that nutrients and phosphorus
from the Amazon outflow stimulate the production of nitrogen-fixing ocean
organisms that convert gaseous nitrogen to amino acids and protein." This
food boosts the production and number of the ocean organisms that absorb greenhouse
gasses from the atmosphere and turn them into organic solids that sink
to the bottom of the sea and die.

The Amazon River has the largest discharge of any of the world's rivers by volume
and is the largest drainage basin on the planet. It accounts for 18 percent of
all river output into the world's oceans. Previously scientists had only studied
the movement of river outflow closer to shore.

"We are really excited about this discovery and are eager to learn if outflow
from the Congo, the world's second largest river, has the same effect on ocean
productivity," Carpenter said.

The team cautions that the quality of the river outflow plume could be negatively
altered by development along the Amazon River. "These organisms are
regulated by the biochemistry of the river and they are sensitive to land-use
alterations and climate change," said Ajit Subramaniam, a co-author and
biological oceanographer at Columbia University. He said activities such as
dam construction and changing agricultural practices could alter the magnitude
of the carbon cycling process.

The study, funded by the National Science Foundation's Biocomplexity in the
Environment program, focused on the content in water samples from 82 stations
in the western tropical North Atlantic Ocean collected between January 2001
and May 2003. Three years of analysis followed. Carpenter studied species
composition and measured the amounts of chlorophyll in the plankton in his
lab at SF State's Romberg Tiburon Center for Environmental Studies.

In addition to Columbia University, Carpenter's colleagues on the study
represented the University of Georgia at Athens, University of Liverpool,
University of Hawaii at Honolulu, State University of New Jersey, Georgia
Institute of Technology, University of Southern California and University
of California, Los Angeles.